Air-pack type contact pressure measuring method

ABSTRACT

While a bag (1) made of a thin, soft, and less elastic material is packed with air and is positioned between contacts of soft materials, a thin tube (2) from the bag (1) is lead to the outside of the contacts, and the pressure difference with respect to atmosphere is measured, whereby the contact pressure of an elastic body can be measured. As water depth (A) (mmH 2  O) is measured while the bag (1) is horizontally sank into the water, and as water temperature is changed while the water temperature is measured, the measured level can be calibrated together with thermal influence.

TECHNICAL FIELD

The present invention relates to contact pressure measurement concerningsoft materials such as external pressure applied to a human body ingarments such as clothes, on a chair, in bedclothes, on a bed, and thelike; and a measuring method in which a bag packed with air is heldbetween contacts, the pressure of the air is measured over time, andthus measured value may be calibrated.

BACKGROUND ART

Conventionally, in the contact pressure measurement for soft materials,there have been no measuring instruments which are accurate and have areproducibility. This is because the state and phenomenon of softsurfaces at the time of contact cannot be comprehended, for example.Also, calibration method for confirming their accuracy has not actuallybeen established yet, thus making it impossible to judge whether eachmeasuring instrument is good or bad.

For example, since strain gauge sensor system is a flat solid sensor, ithas detected a bending stress even when it is simply attached to thesurface of a site in a curved surface of a human body, and has yieldederrors due to surface movement and shifting therebetween when they comeinto contact with each other and due to hindrance to each other uponexpansion and compression. On the other hand, electric resistancesystem, which measures changes in electric resistance upon compressionof an electrically conductive material, is disadvantageous in that itsmaterial is uneven, restoration after compression is slow, and reaction,i.e., resolution, upon strong compression is rough. There have beencases where this system is used with units indicated for thesecharacteristics.

In liquid-pressure equilibration system, which is likely to beconsidered similar to the present invention, a bag in apressure-receiving section is packed with a liquid. Here, zerocorrection is necessary for a pressure sensor, which is connectedthereto via a tube, as well as its altitude. If their relative heightwith respect to each other changes after the correction, an error willoccur. Also, it is unsuitable for dynamic measurement. It is becauseload generated upon acceleration yields an error with respect to theweight of the packed liquid.

Even in the case of a pressure-receiving sensor in which a bag is packedwith air as with the present invention, when the bag uses an elasticmaterial, the area of the surface to be measured always changesaccording to a contact strength, thus failing to achieve comparativemeasurement. In addition, commonly among the above-mentioned measurementsystems, there is a pressure-receiving method in which thepressure-receiving section is formed like interconnected sheets orlattices so as to cover the contact surface. In this case, the softsurface may be restrained from changing its curvature or expanding andcompressing itself, thereby yielding a measured value different from theactual contact state.

DISCLOSURE OF THE INVENTION

The present invention can accurately measure contract pressure of a softsurface and perform calibration for confirming the reproducibility andaccuracy of thus measured value.

A bag made of a thin, soft, and less elastic material is packed withair; and is disposed between contacts, while being lead to the outsideof the contacts via a tube, whereby a contact force can be measured as apressure when a pressure difference between the air and a pressurewithin the bag is measured. The accuracy of the value measured underthis measurement condition is confirmed by water pressure mmH₂ O as thebag is horizontally sank into water. Also, as the water temperature ischanged, thermal influence can be observed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall configurational view showing a measuring method ofthe present invention;

FIG. 2 is a sectional view showing pressure calibration by waterpressure;

FIG. 3 is a sectional view for observing a correlation between pressureand temperature; and

FIG. 4 is a graph showing the correlation between pressure andtemperature measured in FIG. 3.

BEST MODES FOR CARRYING OUT THE INVENTION

In order to describe the present invention in further detail, it will beexplained with reference to the accompanying drawings.

In FIG. 1, a pressure-receiving section comprises a bag 1 made of asoft, nonelastic material; a tube 2, attached thereto, which does notcollapse upon being pressed; and a joint 3. The bag 1 is provided with afilm 4 to be attached to a site, whereas a pressure gauge 5 incorporatestherein a pressure sensor for detecting a pressure difference betweenthe atmosphere and the bag 1. An injection cylinder 6 injects apredetermined amount of air into the bag 1. After the injection, thejoint 3 is connected to the pressure gauge 5, thus attaining a stateready for measurement. For the measurement, the bag 1 is attachedbetween contacts via the attaching film 4 so that the surfaces of thebag 1 totally abut to the contacts. Accordingly, the measurement can beperformed while the bag 1 is attached without being pressed. Here, theattachment film 4 is also effective in protecting the bag 1 fromshifting and abrading.

Thus, in order to measure a soft surface, by use of a softpressure-receiving section, following a curved surface for measurement,the bag 1 made of a nonelastic material whose measuring object does notexpand upon strong pressure is packed with air which is free fromaltitude difference and influence of acceleration, and is lead to theoutside of the contacts via the thin tube 2 that does not impart anythickness influence of the pressure-receiving section to the measuringsurface. Then, the pressure difference with respect to the atmosphere ismeasured by the pressure gauge 5 so as not to be influenced byopening/closing of a door or changes in atmospheric pressure uponweather. Though it is likely to be considered that a large error mayoccur due to thermal influence from the site or the like when thepressure is measured with air, it can be seen from the calibrationmethod of FIG. 3 that such an error is very small.

On the other hand, according to the amount of air injected into the bag1, the range of measurement is determined as follows. In the case wherethe amount is smaller than the maximum volume of the bag 1, when the bag1 has an excess space corresponding to a volume of air expanding due tothe heat from the site or the like, the lower measurable limit is zero,whereas the upper limit is a state where the bag 1 completely collapses.In the case where air is injected into the bag 1 by the maximum volumeof the bag 1 or more, the lower measurable limit is a pressure level atthe time when the air volume including the thermally expanding volume isreduced upon compression to a level not higher than the maximum volumeof the bag 1, whereas the upper limit is a state where the bag 1completely collapses. Accordingly, the lower measurable limit is a statewhere the air injected into the bag 1 is being pressed not by the bag 1but by the mutual contacts. The bag 1 at that time is wrinkled andreduces its volume, thereby functioning to prevent the flatly-expandingair from escaping therefrom. Here, the concentrating stress, changes incurvature, and the like according to the thickness of the bag 1 injectedwith the air are considered to be allowable errors.

Consequently, the contact force of a soft material alleviated byabsorption of its softness per se, deformation thereof, surface tensionof the coating, and the like is always transmitted as a pressure to theair within the bag 1 confined between the contacts, and is guided viathe tube 2 so as to be measured by the pressure sensor.

FIG. 2 shows a method of calibrating thus measured pressure level, inwhich water 11 is introduced into a measuring cylinder 7, the bag 1 isattached to a bottom plate of a T-shaped stick 8 so as to be sank intothe water horizontally, and a water depth A to the bag 1 is measured andthen is calibrated in terms of mmH₂ O. Water 11 is used for calibrationin order to prevent contact resistance from occurring in a surface whichexpands or compresses itself or whose curvature changes. Such contactresistance may occur due to friction, adhering force caused by moisture,adhering force caused by static electricity, and the like, and has noreproducibility or is hard to reproduce. This calibration eliminatessuch resistance and applies a uniform pressure on a horizontal plane.Also, when temperature of water is changed, thermal influence can easilybe seen. Here, though a gas might be used as being pressurized within achamber, the gas is disadvantageous in that it yields a uniform pressurewithin the whole chamber, whereby deformation of the pressure-receivingsection to be calibrated, errors in thickness, and the like cannot beseen, while it is unlikely to yield a uniform temperature change.

In FIG. 3, a tap 10 of a water heater 9 is guided to the bottom of themeasuring cylinder 7, While water 11 is kept spilling over little bylittle, and the water temperature is being measured by a temperaturesensor 12, the bag 1 is attached to the bottom plate of the T-shapedstick 8 and sank into the water, and then the T-shaped stick 8 is fixed.The temperature of water 11 is changed by the water heater 9, and acorrelation between temperature and pressure is observed.

FIG. 4 is a graph showing values measured in FIG. 3. Here, pressurescale 15 whose unit is mmH₂ O, temperature scale 16 whose unit is °C.,and elapsed time 17 indicate the correlation between pressure change 13and water temperature change 14. The thermal influence can be observedas a pressure error not higher than 10 mmH₂ O between 17° C. and 57° C.

INDUSTRIAL APPLICABILITY

Since calibration is also provided in the foregoing measuring method,with a high reliability in measured values, pressure and contraction canbe numerically expressed. For example, the present invention isapplicable to the field of measurement where it is necessary to clarifynot only values depending on difference in softness, values depending onchange in curvature, contact resistance caused by change in moisturesuch as sweat and rain, values depending on change in elasticity; butalso digitization of external pressure influencing each circulatoryorgan within the body, relationship between pressure time and pressurelevel, relationship between pressure area and pressure level, and thelike under a familiar living environment.

It is also applicable to measuring instruments for indicating softnessof sponge or the like and cushioning property of bedclothes, chair, orthe like.

I claim:
 1. A method of detecting a correction value for air-pack typecontact pressure measurement, said method comprising the stepsof:preparing a bag (1) made of a thin, soft, and less elastic materialconnected to a thin pressure-resistant tube (2); injecting apredetermined amount of air into said bag (1); sinking said bag (1), ina horizontal state, to a predetermined depth position into a container(7) containing water; supplying at a predetermined rate into saidcontainer (7) water whose temperature is externally controlled anddischarging water from within said container (7) at said rate so as tokeep the depth of said bag (1) constant; in thus attained state,detecting water temperature near said bag (1) and measuring an airpressure within said bag (1) by a pressure gauge (5), so as to detect arelationship between the pressure within said bag (1) and ambient watertemperature, thereby obtaining temperature correction data for a resultof measurement effected by said pressure gauge (5).
 2. The methodaccording to claim 1, wherein means for heating the water externallysupplied into said container (7) is provided, said heating meanseffecting temperature control of said water.
 3. The method according toclaim 1, wherein said temperature-controlled water is supplied to abottom portion in said container (7) at said predetermined rate, whilewater is discharged from within said container (7) via an upper portionthereof at said rate.
 4. The method according to claim 2, wherein saidtemperature-controlled water is supplied to a bottom portion in saidcontainer (7) at said predetermined rate, while water is discharged fromwithin said container (7) via an upper portion thereof at said rate. 5.The method according to claim 1, wherein a pressure applied to said bag(1) is determined from the depth position of said bag (1) within saidcontainer (7), and thus determined pressure is compared with a valuedetected by said pressure gauge (5), so as to calibrate said pressuregauge (5).
 6. The method according to claim 2, wherein a pressureapplied to said bag (1) is determined from the depth position of saidbag (1) within said container (7), and thus determined pressure iscompared with a value detected by said pressure gauge (5), so as tocalibrate said pressure gauge (5).
 7. The method according to claim 3,wherein a pressure applied to said bag (1) is determined from the depthposition of said bag (1) within said container (7), and thus determinedpressure is compared with a value detected by said pressure gauge (5),so as to calibrate said pressure gauge (5).
 8. The method according toclaim 4, wherein a pressure applied to said bag (1) is determined fromthe depth position of said bag (1) within said container (7), and thusdetermined pressure is compared with a value detected by said pressuregauge (5), so as to calibrate said pressure gauge (5).
 9. An apparatusfor detecting a correction value for air-pack type contact pressuremeasurement, said apparatus comprising:a bag (1) made of a thin, soft,and less elastic material connected to a thin pressure-resistant tube(2) having a joint (3) at a tip thereof; an injection cylinder (6)connectable to said joint (3) and adapted to inject a predeterminedamount of air into said bag (1) via said joint (3) and tube (2); apressure gauge (5) connectable to said joint (3) and adapted to measurea pressure within said bag (1) via said joint (3); a container (7)containing water adapted to sink said bag (1) in a horizontal statetherein; water supplying and discharging means for supplying at apredetermined rate into said container (7) water whose temperature isexternally controlled and discharging water from within said container(7) at said rate so as to keep a depth of said bag (1) constant; andtemperature detecting means for detecting water temperature near saidbag (1) sunk into said container (7); wherein, in a state where said bag(1) is sunk at a predetermined depth position within said container (7),said water supplying and discharging means supplies and dischargeswater, and said pressure gauge (5) measures an air pressure within saidbag (1), so as to detect a relationship between the pressure within saidbag (1) and ambient temperature, thereby obtaining temperaturecorrection data for a result of measurement effected by said pressuregauge (5).
 10. The apparatus according to claim 9, wherein said watersupplying and discharging means has means for heating the waterexternally supplied into said container (7), said heating meanseffecting temperature control of said water.
 11. The apparatus accordingto claim 9, wherein said water supplying and discharging means suppliessaid temperature-controlled water to a bottom portion in said container(7) at said predetermined rate and discharges water from within saidcontainer (7) via an upper edge thereof at said rate.
 12. The apparatusaccording to claim 10, wherein said water supplying and dischargingmeans supplies said temperature-controlled water to a bottom portion insaid container (7) at said predetermined rate and discharges water fromwithin said container (7) via an upper edge thereof at said rate. 13.The apparatus according to claim 9, wherein a pressure applied to saidbag (1) is determined from the depth position of said bag (1) withinsaid container (7), and thus determined pressure is compared with avalue detected by said pressure gauge (5) so as to calibrate saidpressure gauge (5).
 14. The apparatus according to claim 10, wherein apressure applied to said bag (1) is determined from the depth positionof said bag (1) within said container (7), and thus determined pressureis compared with a value detected by said pressure gauge (5) so as tocalibrate said pressure gauge (5).
 15. The apparatus according to claim11, wherein a pressure applied to said bag (1) is determined from thedepth position of said bag (1) within said container (7), and thusdetermined pressure is compared with a value detected by said pressuregauge (5) so as to calibrate said pressure gauge (5).
 16. The apparatusaccording to claim 12, wherein a pressure applied to said bag (1) isdetermined from the depth position of said bag (1) within said container(7), and thus determined pressure is compared with a value detected bysaid pressure gauge (5) so as to calibrate said pressure gauge (5).